(a) Field of the Invention
The present invention relates to an electrophotographic element having a charge generating layer and a charge transport layer formed on an electroconductive substrate, coupled with a process for manufacturing said element, and more particularly it relates to an improvement on the charge generating substances and binders for use in the charge generating layer.
(b) Description of the Prior Art
There have hitherto been proposed a variety of layered electrophotographic elements consisting of an electroconductive substrate, the so-called charge generating layer capable of generating a charge carrier through light absorption which is formed on said substrate and the so-called charge transport layer capable of transferring the thus generated charge carrier by force of an electric field which is superposed on said charge generating layer. In order to improve the electrophotographic characteristics of these layered electrophotographic elements, especially the sensitivity and light fatigue thereof, it is necessary that said charge generating layer be uniform, extremely thin and smooth. Accordingly, application of such processes as (1) depositing a charge generating substance such as Se, Se alloy, organic pigment, etc. through vacuum evaporation (as proposed in, for instance, Japanese Laid-Open Patent Application No. 47838/1973; U.S. Pat. No. 3,973,959), (2) coating a dispersion prepared by dispersing a charge generating substance such as Se, Se alloy, inorganic pigment, organic pigment, etc. in a binder (as proposed in, for instance, Japanese Laid-Open Patent Application No. 18543/1972), (3) coating a solution prepared by dissolving a charge generating substance such as organic pigment in an organic amine (as proposed in, for instance, Japanese Laid-Open Patent Application No. 55643/1977), etc. has been prevalent.
In the case of the foregoing process (1), however, though it can afford a uniform and very thin layer, it is defective in that the cost of the equipment is high and the manufacturing process is difficult to control. In the case of process (2), since various technics for dispersing as well as coating have been established, the element can be manufactured easily and profitably from the viewpoint of cost, but for the purpose of obtaining an extremely thin layer steadily, the dispersibility and the dispersion stability of the dispersion per se come into question. In the case of process (3), the element can be manufactured easily for the same reasons as in the case of process (2), but it involves questions in respect of the safety and the stability of the solution per se, and will result in high cost of equipment.